The sixth nerve is fixed in position at its exit site from the brainstem, located at the inferior border of the pons, and at its entry into the dura of the clivus. Caudal displacement of the brainstem can result in bilateral traction injuries of the sixth nerves as a nonspecific sign of a distantly located, space-occupying disease (supratentorial masses, hemorrhages, or edema, variations in intracranial pressure following lumbar puncture, and idiopathic intracranial hypertension [IIH]). While still in the subarachnoid space or shortly after its entry into the dura, the sixth nerve passes in close proximity to the apex of the petrous bone, the facial nerve, and the trigeminal nerve. Paramastoid inflammatory disease and tumors of the petrous apex produce Grad-enigo syndrome, a sixth nerve palsy accompanied by a deep, boring pain that radiates to the brow and temples. Nasopharyngeal carcinomas that have eaten through the clivus can produce an identical set of symptoms. They can also invade the pterygopalatine fossa, producing dysesthe sias and loss of sensation in the tissues innervated by the infraorbital nerve (Behr's syndrome).
Crushing injuries of the skull with horizontal compression can cause petrous bone fractures with abducens and facial nerve palsy and hemorrhaging from the external auditory canal.
The long intracranial course of the sixth nerve makes it vulnerable to both space-occupying and meningitic inflammatory disease.
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